Manchester United advanced to the FA Cup final in just about the most embarrassing way possible Sunday.

United beat Coventry City in a penalty shootout, but its players hardly celebrated. In a rollicking second half, they had thrown away a three-goal lead, and crumbled under second-division pressure.

In extra time, they nearly capitulated. In the 121st minute, Coventry’s Victor Torp scored, and the sky-blue half of Wembley Stadium exploded, rejoicing in a four-goal comeback and a fairytale for the ages.

But after an agonizing wait, video assistant referees ruled that Coventry’s Haji Wright had been offside in the buildup — by the length of a toe.

United then won on penalties, and booked a date in next month’s final with cross-town rival Manchester City.

But only after collapsing in a way that no Manchester United team had collapsed in over a decade.

United led 2-0 at halftime, and 3-0 by the hour mark. Then Coventry scored in the 71st minute, and United quivered. Muscles tightened. Nerves jangled.

The winningest club in England, one of soccer’s mightiest institutions, was still leading a middling club from England’s second-tier Championship 3-1 — but looked scared.

And then, for 25 minutes, the Red Devils played scared. In the 79th minute, a wicked deflection handed Coventry a second goal. In the 85th minute, United goalkeeper Andre Onana palmed away a stinging drive from Torp — but everybody watching United’s hapless players wobble about knew that more chances were coming.

For the final five minutes of the 90, and then through stoppage time, the underdogs kept ascending. United looked lost, frozen, stupefied.

In the 93rd minute, Aaron Wan-Bissaka conceded a foolish penalty. In the 95th, Wright, a 26-year-old American forward, converted.

When the full-time whistle shrilled to spare United more embarrassment, and red-clad fans booed, players looked shellshocked. For about a minute, as they huddled toward the side of the field, preparing for extra time, manager Erik Ten Hag just stood there, his eyes angled down toward blank turf, as if stuck in a trance.

Ten Hag had botched the second half. His only two subs had been the last two players anybody would want to help kill off a game, aging playmaker Christian Eriksen and useless winger Antony. He had overseen the first blown three-goal lead at United since a meaningless game in 2013. He apparently has the backing of United’s new owners, but he had just witnessed 20 staggering minutes that felt like a tipping point, 20 minutes that epitomized what United has become.

The Red Devils, short-handed and spent, recovered reasonably well in extra time. But the game was even. Balanced. Both teams hit the crossbar. Both sent signals that they were capable of scoring.

Coventry did score, and completed a remarkable encore. In the quarterfinals, Wright had engineered a just-as-stunning comeback, with a 97th-minute assist and 100th-minute goal to beat Wolves.

This was another one. This was a true giant-killing. This was the FA Cup’s best story in years.

Until it wasn’t. VAR ruined the fun. Coventry took a lead in the shootout, then lost it. Tears flowed. Fans didn’t know what to feel.

And the United players? When Rasmus Højlund sealed the shootout, none streamed toward him. Most turned around and shook hands. This, as much as a victory, was a humiliation averted.